java web开发入门七（mybatis）基于intellig idea

mybatis

一、 入门开发步骤

1.导入相关jar包

mybatis3.4.2核心开发包

asm-5.1.jar
cglib-3.2.4.jar
commons-logging-1.1.3.jar
log4j-1.2.17.jar
mybatis-3.4.2.jar

mysql驱动包

mysql-connector-java-5.1.7-bin.jar

2.定义实体及实体映射文件

定义member实体

package com.eggtwo.entity;


import java.math.BigDecimal;
import java.util.Date;

public class Member {
    private int id;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    private String name;
    private int age;
    private Date birthday;
    private boolean man;
    private BigDecimal score;

    public BigDecimal getScore() {
        return score;
    }

    public void setScore(BigDecimal score) {
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public boolean isMan() {
        return man;
    }

    public void setMan(boolean man) {
        this.man = man;
    }
}

定义MemberMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="memberDao">
    <!--
    *******当实体属性和表字段名称一致的话resultMap标签可以省略********
    resultMap标签：映射实体和表关系
    id:映射关系id,要唯一
    type:实体全路径
    -->
    <resultMap id="memberMap" type="com.eggtwo.entity.Member">
        <!--id：映射主键属性
        result:映射非主键属性
        property:实体属性名称
        column:表字段名称
        -->
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <result property="birthday" column="birthday"/>
        <result property="man" column="man"/>
        <result property="score" column="score"/>
    </resultMap>

    <insert id="add" parameterType="com.eggtwo.entity.Member" useGeneratedKeys="true" keyProperty="id">
      insert  into t_member(name,age,birthday,man,score)
       values(#{name},#{age},#{birthday},#{man},#{score})
    </insert>

    <update id="update" parameterType="com.eggtwo.entity.Member">
        update t_member set
        name = #{name},
        age = #{age},
        birthday = #{birthday},
        man = #{man},
        score = #{score}
        where id = #{id}
    </update>

    <delete id="delete" parameterType="int">
        delete from t_member where id = #{id}
    </delete>

    <!-- <select id="getById" parameterType="int" resultType="com.eggtwo.entity.Member">-->
    <!--resultType使用mybatis.xml中设置的别名，这样可以简化难度-->
    <select id="getById" parameterType="int" resultType="memberEntity">
        select id,name,age,birthday,man,score
        from  t_member
        where id=#{id}
    </select>
    <!--
    理论上resultType的值应该是:List<com.eggtwo.entity.Member>
    实际上只需要写List集合中的类型就可以
    -->
    <select id="getAll" resultType="com.eggtwo.entity.Member">
        select *
        from  t_member
    </select>
    <!--分页：多参数的写法-->
    <select id="getPageList" parameterType="map" resultType="com.eggtwo.entity.Member">
        select id,name,age,birthday,man,score
         from t_member limit #{start},#{size}
    </select>
</mapper>

3.定义mybatis.cfg.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- 加载类路径下的属性文件 -->
    <!--加载数据库连接配置信息-->
    <properties resource="jdbc.properties"/>
    <!-- 设置类型别名 -->
    <typeAliases>
        <!--设置实体类Member的别名：memberEntity-->
        <typeAlias type="com.eggtwo.entity.Member" alias="memberEntity"/>
    </typeAliases>

    <!-- 设置一个默认的连接环境信息 -->
    <environments default="mysql_developer">


        <!-- 连接环境信息，取一个任意唯一的名字 -->
        <environment id="mysql_developer">
            <!-- mybatis使用jdbc事务管理方式 -->
            <transactionManager type="jdbc"/>
            <!-- mybatis使用连接池方式来获取连接 -->
            <dataSource type="pooled">
                <!--配置与数据库交互的4个必要属性 -->
                <!-- 直接配置方式，不推荐-->
                <!--<property name="driver" value="com.mysql.jdbc.Driver"/>-->
                <!-- <property name="url" value="jdbc:mysql://127.0.0.1:3306/test"/>-->
                <!--<property name="username" value="root"/>-->
                <!-- <property name="password" value="123456"/>-->


                <!--直接在jdbc.properties文件中配置连接-->
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>

            </dataSource>
        </environment>

    </environments>

    <!-- 加载映射文件-->
    <mappers>
        <mapper resource="com/eggtwo/entity/MemberMapper.xml"/>
    </mappers>
</configuration>

mybatis.cfg.xml加载的jdbc.properties文件

mysql.driver=com.mysql.jdbc.Driver
mysql.url=jdbc:mysql://127.0.0.1:3306/test
mysql.username=root
mysql.password=123456

4.定义mybatis帮助类：MybatisUtil

package com.eggtwo.dao;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;

public class MybatisUtil {

    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    /**
     * 加载位于src/mybatis.xml配置文件
     */
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.cfg.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    /**
     * 禁止外界通过new方法创建
     */
    private MybatisUtil(){}
    /**
     * 获取SqlSession
     */
    public static SqlSession getSqlSession(){
        //从当前线程中获取SqlSession对象
        SqlSession sqlSession = threadLocal.get();
        //如果SqlSession对象为空
        if(sqlSession == null){
            //在SqlSessionFactory非空的情况下，获取SqlSession对象
            sqlSession = sqlSessionFactory.openSession();
            //将SqlSession对象与当前线程绑定在一起
            threadLocal.set(sqlSession);
        }
        //返回SqlSession对象
        return sqlSession;
    }
    /**
     * 关闭SqlSession与当前线程分开
     */
    public static void closeSqlSession(){
        //从当前线程中获取SqlSession对象
        SqlSession sqlSession = threadLocal.get();
        //如果SqlSession对象非空
        if(sqlSession != null){
            //关闭SqlSession对象
            sqlSession.close();
            //分开当前线程与SqlSession对象的关系，目的是让GC尽早回收
            threadLocal.remove();
        }
    }






}

5.定义MemberDao测试mybatis增删查改

 

6.测试

 public static void main(String[] args) throws Exception {
        Connection conn = MybatisUtil.getSqlSession().getConnection();
        System.out.println(conn != null ? "连接成功" : "连接失败");
        MemberDao memberDao = new MemberDao();
        Member member = new Member();
        member.setId(2);
        member.setAge(14);
        member.setName("张三1");
        member.setBirthday(new Date());
        member.setMan(true);
        member.setScore(new BigDecimal(123.24));
        memberDao.add(member);
        //  memberDao.update(member);
        // memberDao.delete(3);
        Member member1 = memberDao.getById(2);
        System.out.println(member1.getName());
        List<Member> memberList = memberDao.getPageList(2,2);
        System.out.println("size:"+memberList.size());
        for (Member m : memberList){
            System.out.println(m.getId());
        }
    }

二、 动态SQL

 1.多条件查询

mapper.xml配置

<select id="getListByWhere" parameterType="map" resultType="com.eggtwo.entity.Member">
    select id,name,age,birthday,man,score
    from t_member
    <where>
        <if test="name!=null and name!=''">
            and name like #{name}
        </if>
        <if test="score!=null">
            and score > #{score}
        </if>
    </where>
</select>

dao调用

 public  List<Member> getListByWhere(String name,BigDecimal score) throws Exception {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            Map<String,Object> map=new LinkedHashMap<>();
            map.put("name",name==null?null: "%"+name+"%");//做like查询
            map.put("score",score);
            List<Member> memberList= sqlSession.selectList("memberDao.getListByWhere",map);
            return  memberList;

        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
        return  null;
    }

测试：

 List<Member> memberList = memberDao.getListByWhere("3",new BigDecimal(30));

2.部分更新字段

mapper.xml配置

<update id="dynamicUpdate" parameterType="map">
        update t_member
        <set>
            <if test="name!=null">
                name = #{name},
            </if>
            <if test="age!=null">
                age = #{age},
            </if>
            <if test="birthday!=null">
                birthday = #{birthday},
            </if>
            <if test="man!=null">
                man = #{man},
            </if>
            <if test="score!=null">
                score = #{score},
            </if>
        </set>
        where id=#{id}
    </update>

dao调用：

public void dynamicUpdate(int id, String name,Integer age,Date birthday,Boolean man,BigDecimal score) throws Exception {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            Map<String,Object> map=new LinkedHashMap<>();
            map.put("id",id);
            map.put("name",name);
            map.put("age",age);
            map.put("birthday",birthday);
            map.put("man",man);
            map.put("score",score);
            sqlSession.update("memberDao.dynamicUpdate", map);
            //提交事务
            sqlSession.commit();

        } catch (Exception e) {
            e.printStackTrace();
            //事务回滚
            sqlSession.rollback();
        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
    }

测试：

memberDao.dynamicUpdate(2,"jack",null,null,false,null);

3.根据id集合或数组不确定删除：delete from table where id in(id1,id2,id3,……)

mapper.xml配置

<!--根据ids数组批量删除数据-->
    <delete id="batchDelete" >
        delete from t_member where id in
        <!--
        循环数组
        解析成：(1,2,34)
        #id表示数组中的每一个元素，名称可以任意写
        -->
        <foreach collection="array" open="(" close=")" separator="," item="id">
            #{id}
        </foreach>
    </delete>
    <!--根据ids列表批量删除数据-->
    <delete id="batchDeleteList" >
        delete from t_member where id in
        <!--
        循环数组
        解析成：(1,2,34)
        #id表示数组中的每一个元素，名称可以任意写
        -->
        <foreach collection="list" open="(" close=")" separator="," item="id">
            #{id}
        </foreach>
    </delete>

dao调用：

public void batchDelete(int[] ids) throws Exception {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.update("memberDao.batchDelete", ids);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            //事务回滚
            sqlSession.rollback();
        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
    }
    public void batchDeleteList(List<Integer> ids) throws Exception {
        SqlSession sqlSession = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.update("memberDao.batchDeleteList", ids);
            sqlSession.commit();
        } catch (Exception e) {
            e.printStackTrace();
            //事务回滚
            sqlSession.rollback();
        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
    }

测试：

 memberDao.batchDelete(new int[]{1,4,5});
        List<Integer> list=new ArrayList<>() ;
        list.add(1);
        list.add(17);
        list.add(18);
        memberDao.batchDeleteList(list);

4.动态插入部分字段

这个不常用

三、 多表查询

 1.一对一映射

班级包t_grade和学生表t_student表

获取学生信息时同时把学生对应的班级信息获取出来

第一步：创建实体

Grade实体

package com.eggtwo.entity;

import java.util.List;

public class Grade {
    private Integer id;
    private String gradeName;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getGradeName() {
        return gradeName;
    }

    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }

}

Student实体

package com.eggtwo.entity;

import java.util.Date;

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private Date birthday;
    private Boolean man;
    private  Grade grade;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public Boolean getMan() {
        return man;
    }

    public void setMan(Boolean man) {
        this.man = man;
    }

    public Grade getGrade() {
        return grade;
    }

    public void setGrade(Grade grade) {
        this.grade = grade;
    }
}

第二步：建立mapper.xml

GradeMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="gradeDao">
    <!--
    *******当实体属性和表字段名称一致的话resultMap标签可以省略********
    resultMap标签：映射实体和表关系
    id:映射关系id,要唯一
    type:实体全路径
    -->
    <resultMap id="gradeMap" type="com.eggtwo.entity.Grade">
        <!--id：映射主键属性
        result:映射非主键属性
        property:实体属性名称
        column:表字段名称
        -->
        <id property="id" column="id"/>
        <result property="gradeName" column="gradeName"/>
    </resultMap>
</mapper>

StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="studentDao">
    <resultMap id="studentMap" type="com.eggtwo.entity.Student">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <result property="birthday" column="birthday"/>
        <result property="man" column="man"/>
        <!--引用GradeMapper.xml中的resultMap，不需要再写一遍映射-->
        <association property="grade" resultMap="gradeDao.gradeMap"/>
    </resultMap>

    <!--返回值类型用resultMap代替resultType，可以解决实体字段类型和表字段类型不一致的问题-->
    <select id="getById" parameterType="int" resultMap="studentMap">
        select s.id,s.name,s.age,s.birthday,s.man,g.id,g.gradeName
        from  t_student s, t_grade g
        where s.gradeId=g.id
        and s.id=#{id}
    </select>

</mapper>

第三步：将mapper.xml加入到mybatis.cfg.xml文件中

    <mappers>
        <mapper resource="com/eggtwo/entity/StudentMapper.xml"/>
        <mapper resource="com/eggtwo/entity/GradeMapper.xml"/>
    </mappers>

第四步：编写StudentDao

package com.eggtwo.dao;

import com.eggtwo.entity.Member;
import com.eggtwo.entity.Student;
import org.apache.ibatis.session.SqlSession;

import java.math.BigDecimal;
import java.sql.Connection;
import java.util.*;

public class StudentDao {
    public Student getById(int id) throws Exception {
        SqlSession sqlSession = null;
        Student student = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            student = sqlSession.selectOne("studentDao.getById", id);

        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
        return student;
    }

    
}

第五步：测试

 public static void main(String[] args) throws Exception {

        StudentDao studentDao = new StudentDao();
        Student s = studentDao.getById(2);
        System.out.println(s.getName());
    }

2.一对多映射

根据班级名称获取学生列表信息

第一步：创建实体

Grade实体

package com.eggtwo.entity;

import java.util.ArrayList;
import java.util.List;

public class Grade {
    private Integer id;
    private String gradeName;
    private List<Student> studentList = new ArrayList<Student>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getGradeName() {
        return gradeName;
    }

    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }

    public List<Student> getStudentList() {
        return studentList;
    }

    public void setStudentList(List<Student> studentList) {
        this.studentList = studentList;
    }
}

Student实体

package com.eggtwo.entity;

import java.util.Date;

public class Student {
    private Integer id;
    private String name;
    private Integer age;
    private Date birthday;
    private Boolean man;
    private  Grade grade;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public Boolean getMan() {
        return man;
    }

    public void setMan(Boolean man) {
        this.man = man;
    }

    public Grade getGrade() {
        return grade;
    }

    public void setGrade(Grade grade) {
        this.grade = grade;
    }
}

第二步：建立mapper.xml

GradeMapper.xml和StudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="gradeDao">
    <!--
    *******当实体属性和表字段名称一致的话resultMap标签可以省略********
    resultMap标签：映射实体和表关系
    id:映射关系id,要唯一
    type:实体全路径
    -->
    <resultMap id="gradeMap" type="com.eggtwo.entity.Grade">
        <!--id：映射主键属性
        result:映射非主键属性
        property:实体属性名称
        column:表字段名称
        -->
        <id property="id" column="id"/>
        <result property="gradeName" column="gradeName"/>
    </resultMap>
</mapper>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="studentDao">
    <resultMap id="studentMap" type="com.eggtwo.entity.Student">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="age" column="age"/>
        <result property="birthday" column="birthday"/>
        <result property="man" column="man"/>
    </resultMap>
    

   
    <select id="getListByGradeName" parameterType="string" resultMap="studentMap">
        select s.id,s.name,s.age,s.birthday,s.man
        from  t_student s, t_grade g
        where s.gradeId=g.id
        and g.gradeName=#{gradeName}
    </select>
</mapper>

第三步：将mapper.xml加入到mybatis.cfg.xml文件中

省略

第四步：编写StudentDao

public List<Student> getListByGradeName(String gradeName) throws Exception {
        SqlSession sqlSession = null;
        List<Student> studentList = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            studentList = sqlSession.selectList("studentDao.getListByGradeName",gradeName);

        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
        return studentList;
    }

第五步：测试

List<Student> studentList = studentDao.getListByGradeName("一班");

3.自定义实体对象（不和数据库表对应）用于接收多表查询出来的复合数据

第一步：定义实体GradeStudent

package com.eggtwo.entity;

import java.util.Date;

public class GradeStudent {
    private Integer gradeId;
    private String gradeName;

    private Integer studentId;
    private String studentName;
    private Integer studentAge;
    private Date studentBirthday;

    public Integer getGradeId() {
        return gradeId;
    }

    public void setGradeId(Integer gradeId) {
        this.gradeId = gradeId;
    }

    public String getGradeName() {
        return gradeName;
    }

    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }

    public Integer getStudentId() {
        return studentId;
    }

    public void setStudentId(Integer studentId) {
        this.studentId = studentId;
    }

    public String getStudentName() {
        return studentName;
    }

    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }

    public Integer getStudentAge() {
        return studentAge;
    }

    public void setStudentAge(Integer studentAge) {
        this.studentAge = studentAge;
    }

    public Date getStudentBirthday() {
        return studentBirthday;
    }

    public void setStudentBirthday(Date studentBirthday) {
        this.studentBirthday = studentBirthday;
    }

    public Boolean getStudentMan() {
        return studentMan;
    }

    public void setStudentMan(Boolean studentMan) {
        this.studentMan = studentMan;
    }

    private Boolean studentMan;
}

第二步：定义GradeStudentMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--映射文件命名空间：要唯一-->
<mapper namespace="gradeStudentDao">
    <resultMap id="gradeStudentMap" type="com.eggtwo.entity.GradeStudent">

        <result property="studentId" column="studentId"/>
        <result property="studentName" column="studentName"/>
        <result property="studentAge" column="studentAge"/>
        <result property="studentBirthday" column="studentBirthday"/>
        <result property="studentMan" column="studentMan"/>
        <result property="gradeId" column="gradeId"/>
        <result property="gradeName" column="gradeName"/>
    </resultMap>

    <!--返回值类型用resultMap代替resultType，可以解决实体字段类型和表字段类型不一致的问题-->
    <select id="getGradeStudentList"  resultMap="gradeStudentMap">
        select s.id as studentId,
        s.name as studentName,
        s.age as studentAge,
        s.birthday as studentBirthday,
         s.man as studentMan,
        g.id as gradeId,
        g.gradeName
        from  t_student s, t_grade g
        where s.gradeId=g.id
    </select>

</mapper>

第三步：将GradeStudentMapper.xml加入mybatis.xml

 <mappers>
        <mapper resource="com/eggtwo/entity/MemberMapper.xml"/>
        <mapper resource="com/eggtwo/entity/StudentMapper.xml"/>
        <mapper resource="com/eggtwo/entity/GradeMapper.xml"/>
        <mapper resource="com/eggtwo/entity/GradeStudentMapper.xml"/>
    </mappers>

第四步：编写dao

public List<GradeStudent> getGradeStudentList() throws Exception {
        SqlSession sqlSession = null;
        List<GradeStudent> gradeStudentList = null;
        try {
            sqlSession = MybatisUtil.getSqlSession();
            gradeStudentList = sqlSession.selectList("gradeStudentDao.getGradeStudentList");

        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            //关闭连接
            MybatisUtil.closeSqlSession();
        }
        return gradeStudentList;
    }